Robot-assisted thoracoscopic surgery for mediastinal tumours in children: a single-centre retrospective study of 149 patients.

OBJECTIVES: The purpose of this retrospective study was to summarize our experience in performing robot-assisted thoracoscopic surgery (RATS) for mediastinal tumours in children to investigate its safety and feasibility. METHODS: This retrospective study involved 149 patients with mediastinal tumours who were hospitalized in the Department of Thoracic Surgery of Beijing Children's Hospital, Capital Medical University, and underwent RATS for tumour resection from March 2021 to November 2022. Information on patient age, weight, tumour size, surgical incision selection, operative time, intraoperative bleeding, intraoperative complications, length of hospital stay, rate of conversion to thoracotomy and follow-up conditions were summarized. RESULTS: All 149 surgeries were successfully completed with no cases of mortality. There were 77 male and 72 female patients, with a mean age of 5.9 years (range: 6 months-16 years, 8 months) and a mean weight of 23.6 kg (8.0-72.0 kg). The mean maximum tumour diameter was 5.5 cm (2.0-12.0 cm), the mean operative time was 106.7 min (25.0-260.0 min), the mean intraoperative bleeding volume was 11.3 ml (1.0-400.0 ml) and the mean hospital stay was 7.2 days (4.0-14.0 days). All patients recovered well with no cases of tumour recurrence or mortality during the postoperative follow-up period (3-23 months). CONCLUSIONS: RATS is safe and feasible to apply in children with mediastinal tumours who are >6 months of age and weigh more than 8 kg in terms of short-term outcomes, but longer-term follow-up is needed to fully evaluate the benefits. For cases that are associated with greater surgical difficulty and risk, a comprehensive surgical plan should be fully prepared in advance of surgery.

Disentangling the activity-selectivity trade-off in catalytic conversion of syngas to light olefins.

Breaking the trade-off between activity and selectivity has been a long-standing challenge in the field of catalysis. We demonstrate the importance of disentangling the target reaction from the secondary reactions for the case of direct syngas conversion to light olefins by incorporating germanium-substituted AlPO-18 within the framework of the metal oxide-zeolite (OXZEO) catalyst concept. The attenuated strength of the catalytically active Brønsted acid sites allows enhancing the targeted carbon-carbon coupling of ketene intermediates to form olefins by increasing the active site density while inhibiting secondary reactions that consume the olefins. Thus, a light-olefins selectivity of 83% among hydrocarbons and carbon monoxide conversion of 85% were obtained simultaneously, leading to an unprecedented light-olefins yield of 48% versus current reported light-olefins yields of ≤27%.

Steering the reaction pathway of syngas-to-light olefins with coordination unsaturated sites of ZnGaOx spinel.

Significant progress has been demonstrated in the development of bifunctional oxide-zeolite catalyst concept to tackle the selectivity challenge in syngas chemistry. Despite general recognition on the importance of defect sites of metal oxides for CO/H2 activation, the actual structure and catalytic roles are far from being well understood. We demonstrate here that syngas conversion can be steered along a highly active and selective pathway towards light olefins via ketene-acetate (acetyl) intermediates by the surface with coordination unsaturated metal species, oxygen vacancies and zinc vacancies over ZnGaOx spinel-SAPO-34 composites. It gives 75.6% light-olefins selectivity and 49.5% CO conversion. By contrast, spinel-SAPO-34 containing only a small amount of oxygen vacancies and zinc vacancies gives only 14.9% light olefins selectivity at 6.6% CO conversion under the same condition. These findings reveal the importance to tailor the structure of metal oxides with coordination unsaturated metal sites/oxygen vacancies in selectivity control within the oxide-zeolite framework for syngas conversion and being anticipated also for CO2 hydrogenation.

Clinical characteristics and prognosis of pulmonary inflammatory myofibroblastic tumor: An over 10-year retrospective analysis.

IMPORTANCE: Pulmonary inflammatory myofibroblastic tumors (PIMTs) are primary lung tumors in children. Misdiagnosis easily occurs because of the nonspecific clinical manifestations, laboratory examination results, and imaging findings in affected patients. OBJECTIVE: To summarize the clinical characteristics, diagnosis, and prognosis of children with PIMTs. METHODS: This retrospective analysis included 23 children with PIMTs who received treatment in our hospital from January 2008 to January 2019. The clinical manifestations, laboratory examination results, and computed tomography findings were retrospectively analyzed. RESULTS: The population included 13 boys and 10 girls, with a median age at onset of 78 months (range, 10-126 months). Fourteen patients had PIMT lesions in the right lung and nine patients had PIMT lesions in the left lung. The surgical procedures included pulmonary wedge resection, pulmonary lobectomy, and total pneumonectomy. The median operation time was 115 min (range, 45-235 min); the median intraoperative blood loss volume was 30 mL (range, 3-500 mL). During the operation, one patient each had pulmonary hemorrhage, vena cava hemorrhage, and thoracic duct injury. Postoperative complications included pulmonary embolism in one patient and tumor recurrence in two patients; neither of these complications recurred after reoperation. The median follow-up period was 49 months (range, 2-127 months). INTERPRETATION: Children with PIMTs exhibited good prognoses and primarily underwent surgical resection as treatment. Complete preoperative evaluation should be performed in affected patients.

Diagnosis and treatment of pleuropulmonary blastoma in children: A single-center report of 41 cases.

OBJECTIVE: This study was performed to investigate the age at onset, clinical manifestations, pathological types and features, treatment, and prognosis of pleuropulmonary blastoma (PPB) in children in an attempt to reduce the misdiagnosis rate and achieve early detection and timely intervention. METHODS: We retrospectively studied the clinical data of 41 pediatric patients with PPB who were treated in our center from March 2002 to November 2018. The data comprised the age at onset, clinical manifestations, characteristics of familial diseases, pathological types, surgical procedures, and prognosis. RESULTS: Twenty male and 21 female patients were included, with a 0.95:1.00 male:female ratio. In total, 51.2% of the patients were misdiagnosed as having nonneoplastic lesions at the first presentation. The interval from symptom onset to surgery/chemotherapy ranged from 5 to 210 days. The pathological types were type I (cystic) PPB (n = 5, 11.9%), for which the median age at diagnosis was 21 months (range, 8-24 months); (solid/cystic) II PPB (n = 12, 28.6%), for which the median age at diagnosis was 37 months (range, 22-112 months); and type III (solid) PPB (n = 23, 54.8%), for which the median age at diagnosis was 39 months (range, 19-156 months). The pathologic type was undefined in one patient (2.4%). The patients were mainly treated by surgery and chemotherapy. The 5-year disease-free survival rate was 69.2%. CONCLUSION: The clinical manifestations of PPB are nonspecific, its misdiagnosis rate is high, and it has a poor prognosis. Pediatricians should be aware of the seriousness of PPB. The possibility of PPB should be considered in children with pneumothorax, multiple pulmonary cystic lesions, a family history of pulmonary cysts, a family history of PPB, or space-occupying lesions associated with DICER1 syndromes. The lesion should be closely monitored and surgically removed if necessary. The nature of the lesion should be identified early to minimize the risk of progression of the PPB to worse types because of misdiagnosis and missed diagnosis. Multidisciplinary treatment including surgery, chemotherapy, and/or radiotherapy can be applied to patients with PPB. TYPE OF STUDY: Treatment study. LEVEL OF EVIDENCE: Level III.

Application of an Extracorporeal-Assisted Intracorporeal Sliding Knot-Tying Technique in Minimally Invasive Surgery in Children.

Background: A retrospective study was carried out to determine the feasibility and safety of an extracorporeal-assisted intracorporeal sliding knot-tying technique in minimally invasive surgery in children. Materials and Methods: From June 2009 to December 2017, a total of 333 cases of pediatric minimally invasive surgery were performed using the extracorporeal-assisted intracorporeal sliding knot-tying technique. Polyester, polyglactin, and polydioxanone sutures were used for suturing and knotting. The average time used for knotting was recorded during the surgery. The patients were followed up for unraveled knots and recurrence of the diseases. Results: All 333 surgical procedures were performed successfully, including 152 cases of thoracoscopic diaphragmatic hernia repair, 151 cases of thoracoscopic diaphragmatic plication, 7 cases of thoracoscopic esophageal anastomosis, and 23 cases of laparoscopic esophageal hiatal hernia fundoplication. No serious complications or mortalities were observed. Twelve-month to 9-year follow-up showed that all pediatric patients recovered well and no recurrence or unraveled knots were found. Conclusions: This new knot-tying technique is safe and feasible for various minimally invasive endoscopic surgeries, especially for suturing tissues under tension, such as thoracoscopic diaphragmatic hernia repair, laparoscopic esophageal hiatal hernia repair, and fundoplication. All types of sutures can be used for this knot-tying technique. It is easy to learn and can be quickly mastered by doctors with endoscopic surgery experience.

Different Nuss procedures and risk management for pectus excavatum after surgery for congenital heart disease.

PURPOSE: In Nuss procedure for pectus excavatum (PE) after surgery for congenital heart disease (CHD), retrosternal adhesion may increase the risk of cardiac injury. This study aimed to explore different Nuss procedures and their implications for reducing the incidence of serious complications and improving surgical safety. METHODS: We retrospectively reviewed 49 cases (29 male and 20 female) of Nuss procedures for PE after surgery for CHD that were performed between April 2003 and December 2016. The median age was 5.8 years (range, 3.0-17.9), and the median Haller index was 4.6 (3.2-17.7). All patients were evaluated on their cardiac function and severity of PE by echocardiography and computed tomography scan, respectively. Three surgical procedures were used. Perioperative conditions were analyzed, including CHD type, interval between two operations, blood loss, operation time, hospital stay, complications, and postoperative results. RESULTS: All 49 cases were completed successfully. Fourteen cases (28.6%) involved the standard three-incision thoracoscopic Nuss procedure, 30 cases (61.2%) involved the Nuss procedure assisted by a median sternum incision, and 5 cases (10.2%) involved the Nuss procedure with sternal suspension. The median interval between the CHD surgery and Nuss procedure was 4.0 years (0.5-12.0). The median blood loss was 2.0 mL (1.0-150.0 mL). The median operation time was 45.0 min (27.0-230.0), and the median hospital stay was 6.0 days (5.0-9.0). Three patients (6.1%) experienced severe surgical complications: 2 experienced a rupture of the right atrium and 1 had pericardial injury. Patients were followed up for 7-120 months after surgery. The postoperative results were excellent in 46 cases (93.9%) and good in 3 (6.1%). Twenty-four of the 49 patients have had their bars removed. The median time for bar removal was 36.0 months (24.0-47.0). The outcome after bar removal surgery was excellent in 20 cases and good in 4. CONCLUSIONS: Patients may develop PE or worsening of preexisting PE after open heart surgery for CHD. Surgery for PE can still be performed by the standard Nuss technique without increasing the risk of cardiac injury for the patients that have had interventional cardiology procedures for CHD previously. However, the risk of cardiac injury during the Nuss procedure dramatically increases due to retrosternal adhesions that develop after open heart surgery for CHD. In our experience, the Nuss procedure is safe and feasible after open heart surgery for CHD when performed by an experienced pectus surgeon using an individualized surgical plan for each patient. TYPE OF STUDY: Retrospective study. LEVEL OF EVIDENCE: Level IV.

Effects of trimethylsilane plasma coating on the hydrophobicity of denture base resin and adhesion of Candida albicans on resin surfaces.

STATEMENT OF PROBLEM: Candida-associated denture stomatitis is the most common oral mucosal lesion among denture wearers. Trimethylsilane (TMS) plasma coating may inhibit the growth of Candida albicans on denture surfaces. PURPOSE: The purpose of this in vitro study was to investigate whether TMS plasma coatings can effectively reduce C albicans adhesion on denture base acrylic resin surfaces. MATERIAL AND METHODS: Sixty denture base acrylic resin disks with smooth and rough surfaces were prepared and were either left untreated (control group) or coated with TMS monomer (experimental group) by using plasma. Contact angles were measured immediately after TMS plasma coating. The morphology of C albicans adhesion was observed with scanning electron microscopy (SEM). Energy-dispersive spectroscopy (EDS) was used to characterize the elemental composition of the specimen surface. An adhesion test was performed by incubating the resin disk specimens in C albicans suspensions (1×107 cells/mL) at 37°C for 24 hours and further measuring the optical density of the C albicans by using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay test. One-way ANOVA and 2-way ANOVA were followed by a post hoc test analysis (α=.05). RESULTS: The group with TMS coating exhibited a more hydrophobic surface than the control group. EDS analysis revealed successful TMS plasma coating. The difference in the mean contact angles between the uncoated group and the TMS-coated group was statistically significant (P<.05), 79.0 ±2.9 degrees versus 105.7 ±1.5 degrees for the smooth surface and 90.2 ±7.6 degrees versus 131.5 ±2.1 degrees for the rough surface. In SEM analysis, the C albicans biofilm was found to grow more on the surface of the denture base resin without the TMS coating than on the surfaces of the experimental group. In the adhesion test, the amount of C albicans adhering to the surface of denture base resin with the TMS coating was significantly less than that on the surfaces without TMS coating (P<.05). CONCLUSIONS: TMS coating significantly reduced the adhesion of C albicans to the denture base resin and may reduce denture stomatitis.

Hydroxyapatite induces spontaneous polymerization of model self-etch dental adhesives.

The objective of this study is to report for the first time the spontaneous polymerization phenomenon of self-etch dental adhesives induced by hydroxylapatite (HAp). Model self-etch adhesives were prepared by using a monomer mixture of bis[2-(methacryloyloxy)ethyl] phosphate (2MP) with 2-hydroxyethyl methacrylate (HEMA). The initiator system consisted of camphorquinone (CQ, 0.022 mmol/g) and ethyl 4-dimethylaminobenzoate (4E, 0.022-0.088 mmol/g). HAp (2-8 wt.%) was added to the neat model adhesive. In a dark environment, the polymerization was monitored in-situ using ATR/FT-IR, and the mechanical properties of the polymerized adhesives were evaluated using nanoindentation technique. Results indicated that spontaneous polymerization was not observed in the absence of HAp. However, as different amounts of HAp were incorporated into the adhesives, spontaneous polymerization was induced. Higher HAp content led to higher degree of conversion (DC), higher rate of polymerization (RP) and shorter induction period (IP). In addition, higher 4E content also elevated DC and RP and reduced IP of the adhesives. Nanoindentation result suggested that the Young's modulus of the polymerized adhesives showed similar dependence on HAp and 4E contents. In summary, interaction with HAp could induce spontaneous polymerization of the model self-etch adhesives. This result provides important information for understanding the initiation mechanism of the self-etch adhesives, and may be of clinical significance to strengthen the adhesive/dentin interface based on the finding.

Enhancement in dentin collagen's biological stability after proanthocyanidins treatment in clinically relevant time periods.

OBJECTIVE: To investigate whether proanthocyanidins (PA) is capable of improving dentin collagen's biological stability through cross-linking within time periods that are clinically relevant. MATERIALS AND METHODS: Demineralized dentin collagen slabs were treated with 3.75 wt% PA solution for 10s, 1 min, 30 min, 60 min, 120 min, 360 min, and 720 min, respectively. The resultant cross-linked collagen samples were subject to digestion with 0.1% collagenase at 37°C for 2h, 6h, 12h, 24h, 36 h, and 48 h. The percentage of weight loss after digestion was calculated to evaluate PA-treated collagen's resistance toward enzymatic degradation. Fourier-transformed infrared (FTIR) spectroscopy was used to probe evidences of PA-collagen interactions after various periods of PA treatment. RESULTS: The collagenase digestion assay suggests that PA treatment as short as 10s can enhance collagen's resistance toward enzymatic challenge. The FTIR spectroscopy further verifies that PA is indeed incorporated into collagen regardless of treatment time, possibly via a mechanism involving the chemical interactions between PA and collagen. SIGNIFICANCE: This study confirmed that PA can effectively cross-link collagen and improve its biological stability in time periods as short as 10s. The use of PA as a priming agent is therefore clinically feasible and is a promising approach to improving the durability of current dentin bonding systems.

BisGMA/TEGDMA dental nanocomposites containing glyoxylic acid-modified high-aspect ratio hydroxyapatite nanofibers with enhanced dispersion.

The purpose of this research was to investigate the influence of the glyoxylic acid (GA) modification of hydroxyapatite (HAP) nanofibers on their dispersion in bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) dental composites and also to investigate the mechanical properties, water absorption and water solubility of the resulting dental resins and composites. Scanning/transmission electron microscopy images showed that microsized HAP nanofiber bundles could be effectively broken down into individual HAP nanofibers with an average length of ∼15 µm after the surface modification process. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and thermal gravimetric analysis characterization confirmed that GA was chemically grafted on the HAP nanofiber surface, hypothetically by reacting with the amine group on the HAP nanofiber surface. The enhanced dispersion of HAP nanofibers in the dental matrix led to increased biaxial flexural strength (BFS) compared with the corresponding dental resins and composites filled with untreated HAP nanofibers. In addition, impregnation of small mass fractions of the GA-modified HAP nanofibers into the BisGMA/TEGDMA dental resins (5 wt%, 10 wt%) or composites (2 wt%, 3 wt%) could also substantially improve the BFS in comparison with the controls (pure resins or dental composites filled with silica particles alone). Larger mass fractions could not increase the mechanical property further or even degraded the BFS values. Water behavior testing results indicated that the addition of the GA-modified HAP nanofibers resulted in higher water absorption and water solubility values, which are not preferred for clinical application. In summary, well-dispersed HAP nanofibers and their dental composites with enhanced mechanical properties have been successfully fabricated, but the water absorption and water solubility of such dental composites need to be further improved.

Identification of a protein-containing enamel matrix layer which bridges with the dentine-enamel junction of adult human teeth.

OBJECTIVE: To investigate the ultrastructure and chemical composition of the dentine-enamel junction and adjacent enamel of minimally processed third molar tooth sections. DESIGN: Undecalcified human third molar erupted teeth were sectioned and etched with 4% EDTA or 37% phosphoric acid prior to visualization by scanning electron microscopy. Confocal Raman spectroscopy was carried out at 50 µm and more than 400 µm away from the dentine-enamel junction before and after mild etching. RESULTS: A novel organic protein-containing enamel matrix layer was identified for the first time using scanning electron microscopy of etched bucco-lingual sections of crowns. This layer resembles a three-dimensional fibrous meshwork that is visually distinct from enamel "tufts". Previous studies have generally used harsher solvent conditions which likely removed this layer and precluded its prior characterization. The shape of the organic enamel layer generally reflected that of sheath regions of enamel rods and extended from the dentine-enamel junction about 100-400 µm into the cuspal enamel. This layer exhibited a Raman CH stretching peak at ∼2931 cm(-1) characteristic of proteins and this signal correlated directly with the presence and location of the matrix layer as identified by scanning electron microscopy. CONCLUSIONS: The enamel protein layer was most prominent close to the dentine-enamel junction and was largely absent in cuspal enamel >400 µm away from the dentine enamel junction. We hypothesize that this protein containing matrix layer could provide an important biomechanical linkage between the enamel and the dentine-enamel junction and by extension, with the dentine, of the adult tooth (246 words).

Chemical characterization of etched dentin in non-carious cervical lesions.

PURPOSE: Bonding to non-carious cervical lesion (NCCL) sclerotic dentin that involves acid etching continues to be a challenging problem due to its altered chemical structure. In the present study, the objective was to investigate the chemical response of NCCL sclerotic dentin to the different acid etching times. MATERIALS AND METHODS: Extracted human premolars affected with NCCLs were selected, and a cavity matching the natural lesion with respect to size and location was prepared on the lingual surface of each tooth to serve as the control. The dentin surfaces were treated for 15 s and 30 s using 37% phosphoric acid and then analyzed by Raman microspectroscopic mapping/imaging. RESULTS: NCCL dentin substrates had dramatic effects on the chemical profile of dentin demineralization. The spectral comparison showed that the demineralized layer generated by the acid treatment was highly irregular in terms of depth and mineral component retained, especially when NCCL sclerotic dentin was etched for 15 s. When the etching time was increased to 30 s, the demineralization of NCCL sclerotic dentin was more effective and comparable to the nonsclerotic control that was treated for 15 s. Different etching times affected the depth, degree, and profile of the dentin demineralization. CONCLUSION: The shorter etching time (ie, 15 s) might not be adequate for NCCL sclerotic dentin. However, the longer etching time (ie, 30 s) would induce much deeper demineralized dentin for nonsclerotic substrates. Thus, although extended etching times can be used to remove the hypermineralized layer, further studies are required to analyze the impact this might have on the dentin bonding.

Collagen cross linking increases its biodegradation resistance in wet dentin bonding.

PURPOSE: The biodegradation of exposed dentin collagen within the adhesive/dentin (a/d) interface is one of the main reasons for composite restoration failures and seriously affects the durability of dental restorations. In the present study, the objective was to investigate whether the inclusion of the cross-linking reagent (glutaraldehyde, GA) in the adhesive would increase collagen biodegradation resistance within the a/d interface. MATERIALS AND METHODS: The model adhesive consisted of ~60 % monomers (HEMA/bis-GMA, 45/55 wt/wt) and ~ 40 % ethanol as a solvent. 5% GA was added to the above formulation. After the dentin surfaces were etched for 15 s with 35% phosphoric acid, rinsed with water and blotted dry, adhesives both with and without GA were applied and polymerized by visible light for 20 s. These a/d specimens were immersed in the biodegradation solution (prepared by adding 160 mg collagenase in 1 liter of TESCA buffer solution) for up to 30 days after proceeding with the sectioning/fracture to expose the a/d interfaces. The specimens were analyzed using SEM and micro-Raman spectroscopy. RESULTS: SEM results indicated that for the adhesive without GA, there were many voids and a loss of collagen fibrils in the a/d interface after being challenged by the biodegradation solution. The Raman spectra collected from the interface showed that the amide I of collagen at 1667 cm-1 obviously decreased, indicating a removal of collagen fibrils during the degradation process. For the adhesive containing GA, the collagen fibrils within the interface did not degrade at all, which was also confirmed by the Raman results. CONCLUSION: The results corroborate the previous findings that by using the current adhesive system and wet bonding, the collagen fibrils in the a/d interface are largely unprotected and easily undergo biodegradation. Directly including cross-linking agents in the adhesive could protect collagen fibrils from degradation in situ within the a/d interface.

Chemical composition and structure of peritubular and intertubular human dentine revisited.

OBJECTIVE: Currently there is still a debate about whether peritubular dentine (PTD) is non-collageneous or collageneous tissue. The chemical composition and structure of human PTD and intertubular dentine (ITD) was re-visited in this study. DESIGN: The dentine tubular region including ITD and PTD prepared from human third molars was in situ detected by means of micro-Raman spectroscopy (µRs) and atomic force microscopy (AFM). RESULTS: From the µRs study, it was found that the mineral/matrix ratios (phosphate vs. CH(2)) in PTD were ∼3 times of those in ITD. For the mineral, the differences between PTD and ITD were small, but still detectable. For the organic matrix, the intensity ratios of amide III to CH(2) in ITD were ∼1.5 times of those in PTD, indicating the structural differences. In addition, there was a higher proline/hydroxyproline content in ITD than that in PTD. However, the overall Raman peak contour in the amide regions (I & III) was similar, indicating collagen might still exist in both the ITD and PTD. An in situ AFM observation of the dentinal tubular region during EDTA etching confirmed that dentine collagen ran across from the ITD into the PTD. CONCLUSION: A phenomenon similar to that observed in the dentine-enamel junction is proposed to explain the above results. It is demonstrated that the µRs-AFM approach can be used to provide an insight into the structure of small dental tissues at the micron or sub-micron scale.

The Distribution of Carbonate in Enamel and its Correlation with Structure and Mechanical Properties.

The correlation of carbonate content with enamel microstructure (chemical and crystal structure) and mechanical properties was evaluated via linear mapping analyses using Raman microspectroscopy and nanoindentation. Mappings started at the outer enamel surface and ended in the inner enamel near the dentin-enamel junction (DEJ) in lingual and buccal cervical and cuspal regions. The carbonate peak intensity at 1070 cm-1 gradually increased from outer to inner enamel. Moreover, the phosphate peak width, as measured by the full width at half maximum (FWHM) of the peak at 960 cm-1, also increased, going from ~9 cm-1 in outer enamel to ~13 cm-1 in enamel adjacent to the DEJ, indicating a decrease in the degree of crystallinity of hydroxyapatite from outer to inner enamel. In contrast, Young's modulus decreased from 119±12 to 80±19 GPa across outer to inner enamel with a concomitant decrease in enamel hardness from 5.9±1.4 to 3.5±1.3 GPa. There were also significant correlations between carbonate content and associated crystallinity with mechanical properties. As carbonate content increased, there was an associated decrease in crystallinity and both of these changes correlated with decreased modulus and hardness. Collectively, these results suggest that enamel carbonate content and the associated change in the crystal structure of hydroxyapatite, i.e. degree of crystallinity, may have a direct effect on enamel mechanical properties. The combination of Raman microspectroscopy and nanoindentation proved to be an effective approach for evaluating the microstructure of enamel and its associated properties.

Cross-linked demineralized dentin maintains its mechanical stability when challenged by bacterial collagenase.

The molecular structure, weight loss, and mechanical properties of demineralized dentin of noncrosslinked/crosslinked by glutaraldehyde (GA) were investigated when being challenged by bacterial collagenase solution over time in this study. Raman spectra proved that crosslinking occurred in demineralized dentin matrices after being treated with GA. Meanwhile, the weight of the cross-linked demineralized dentin matrices did not change after being challenged by bacterial collagenase solution up to 1 week. However, the weight of noncross-linked dentin collagen fell by almost 45% after degradation for 5 h, and up to 100% after 19 h. The tensile strength of demineralized dentin matrices did not show a significant change after being crosslinked, while the stiffness of demineralized dentin matrices showed more improvement than that of noncross-linked collagen. The toughness of demineralized dentin matrices decreased slightly after being crosslinked. Importantly, neither the tensile strength of GA-cross-linked demineralized dentin nor its stiffness changed over time in either control buffer or collagenase solution compared with that of noncross-linked controls. These results suggested that improving the degree of crosslinking in dentin collagen could be one method to inhibit its biodegradation and further to increase the durability of dental restorations.

Comparison of flexural properties and surface roughness of nanohybrid and microhybrid dental composites.

Recently introduced nanohybrid dental composites have promised a smoother surface finish and strength, comparable to that of microhybrid composites. This study compared the mechanical properties and surface finish of nanohybrid and microhybrid composites by measuring the flexural strength and modulus (four-point bend) and surface roughness after polishing (using atomic force microscopy) of six commercial dental composites (three nanohybrid, three microhybrid). Scanning electron microscopy (SEM) was used to qualitatively characterize filler morphology and size. The flexural strength and modulus were significantly higher among the microhybrid composites, while the nanohybrid composites exhibited significantly lower surface roughness. SEM characterization revealed differences in filler particle size and shape that could affect the flexural properties and surface roughness. Composites containing spherical filler particles exhibited higher flexural properties and lower roughness values compared to composites with irregular fillers. These results did not support the premise that nanohybrid composites offer similar mechanical properties to microhybrids in addition to a better surface finish.

Dentin surface treatment using a non-thermal argon plasma brush for interfacial bonding improvement in composite restoration.

The objective of this study was to investigate the treatment effects of non-thermal atmospheric gas plasmas on dentin surfaces used for composite restoration. Extracted unerupted human third molars were prepared by removing the crowns and etching the exposed dentin surfaces with 35% phosphoric acid gel. The dentin surfaces were treated using a non-thermal atmospheric argon plasma brush for various periods of time. The molecular changes of the dentin surfaces were analyzed using Fourier transform infrared spectrophotometry/attenuated total reflectance (FTIR/ATR), and an increase in the amount of carbonyl groups was detected on plasma-treated dentin surfaces. Adper Single Bond Plus adhesive and Filtek Z250 dental composite were applied as directed. To evaluate the dentin/composite interfacial bonding, the teeth thus prepared were sectioned into micro-bars and analyzed using tensile testing. Student-Newman-Keuls tests showed that the bonding strength of the composite restoration to peripheral dentin was significantly increased (by 64%) after 30 s of plasma treatment. However, the bonding strength to plasma-treated inner dentin did not show any improvement. It was found that plasma treatment of the peripheral dentin surface for up to 100 s resulted in an increase in the interfacial bonding strength, while prolonged plasma treatment of dentin surfaces (e.g. 5 min) resulted in a decrease in the interfacial bonding strength.

Grape seed proanthocyanidins increase collagen biodegradation resistance in the dentin/adhesive interface when included in an adhesive.

OBJECTIVES: Contemporary methods of dentin bonding could create hybrid layers (HLs) containing voids and exposed, demineralised collagen fibres. Proanthocyanidins (PA) have been shown to cross-link and strengthen demineralised dentin collagen, but their effects on collagen degradation within the HL have not been widely studied. The purpose of this study was to compare the morphological differences of HLs created by BisGMA/HEMA model adhesives with and without the addition of grape seed extract PA under conditions of enzymatic collagen degradation. METHODS: Model adhesives formulated with and without 5% PA were bonded to the acid etched dentin. 5-µm-thick sections cut from the bonded specimens were stained with Goldner's trichrome. The specimens were then exposed to 0.1% collagenase solution for 0, 1, or 6 days. Following collagenase treatment, the specimens were analysed with SEM/TEM. RESULTS: Staining did not reveal a difference in the HLs created with the two adhesives. SEM showed the presence of intact collagen fibrils in all collagenase treatment conditions for specimens bonded with adhesive containing PA. These integral collagen fibrils were not observed in the specimens bonded with adhesive without PA after the same collagenase treatment. TEM confirmed that the specimens containing PA still showed normal collagen fibril organisation and dimensions after treatment with collagenase solution. In contrast, disorganised collagen fibrils in the interfacial zone lacked the typical cross-banding of normal collagen after collagenase treatment for specimens without PA. CONCLUSIONS: The presence of grape seed extract PA in dental adhesives may inhibit the biodegradation of unprotected collagen fibrils within the HL.